1. Field of the Invention
The invention relates to an onboard fuel cell system that is suited to be installed in vehicles such as automobiles and the like, and to a method of discharging hydrogen-off gas.
2. Description of Related Art
Fuel cells, which generate electric power by being supplied with hydrogen gas from high-pressure hydrogen gas tanks, hydrogen-occluding alloy tanks, or the like, exhibit high energy efficiency and thus are promising as a power source for electric vehicles and the like.
In the case where such a fuel cell is used as a power source for a vehicle, the vehicle requires being equipped with a fuel cell system including not only a fuel cell but also a hydrogen gas-supplying source such as the high-pressure hydrogen gas tank or the hydrogen-occluding alloy tank as mentioned above, and hydrogen gas flow passages for delivering hydrogen gas to the fuel cell from the hydrogen gas-supplying source.
Because a fuel cell system to be installed in a vehicle uses highly combustible hydrogen gas, it is necessary to pay careful attention in handling hydrogen gas. However, not much attention has been paid to hydrogen-off gas that has already been consumed to generate electric power in the fuel cell. That is, although this hydrogen-off gas contains unconsumed hydrogen, it is in fact discharged to the atmosphere directly.
In view of such circumstances, the inventors have recognized a new problem described below and decided to tackle it.
Gases containing hydrogen are combustible. Therefore, if the concentration of hydrogen in gases discharged to the atmosphere is increased while something that could act as an ignition source is located close to an exhaust port through which the gases are discharged, there is a danger that hydrogen-off gas will catch fire.